Mini Mushroom
The Mini Mushroom is a variety of Mushrooms found in the Mushroom Kingdom. Whoever uses it will shrink greatly in size, becoming as tiny as a mouse. The Mini Mushroom debuted in Super Mario Kart, where Toad and Peach shot them out at players. If touched, it would shrink the driver making him easy to run over.
It was later seen in Mario Party 4 as a pink capped shroom that reduced the Dice Block to 1-5 and allowed a person under its effects to enter Gates and play Mini Mini-games. Additionally, it had an alternate form called Super Mini Mushroom that did the same, but with two Dice Blocks.
They recently reappeared in New Super Mario Bros., where they were light blue, and they shrunk Mario and Luigi's size greatly and yet again gave them the ability to enter tiny Warp Pipes. They also gained the abilities to perform Floaty Jumps and run across water, thanks to their very light weight. If Mario or Luigi (in Mini form) is able to defeat the Mummipokey, then he will gain acsess to World 4. If he beats Petey Piranha in Mini form, he can go to World 7.